The invention relates to a system and a method for reactive power compensation in electrical power networks.
Electrical power networks are used for transmitting and distributing electricity for various purposes. These networks experience voltage variations during operation that are caused by the variation in generation of active and reactive power by different power generating devices and variable consumption of active and reactive power by different loads in the electrical power network.
Electrical power networks may have large and fast voltage variations (for example, due to increasing amount of intermittent renewable energy) that may result in excessive operation of voltage regulating devices such as on-load tap changing transformers, voltage regulators and capacitors. Excessive operation of mechanically-switched transformer taps and capacitors may lead to increased maintenance and diminished operating life of these devices.
One existing approach for mitigating the voltage variation is to provide a closed-loop voltage control. For example, in some renewable power generation systems, a closed-loop controller adjusts a power factor of a power converter to provide the reactive power needed for mitigating the voltage variation. The closed-loop controller, however, may undesirably interact with other reactive power sources and voltage regulating devices in the electrical power network during this process. Furthermore, the closed-loop controller may tend to compensate for the reactive power demand of the network and connected loads, which may result in increased losses in the source of reactive power and sub-optimal utilization of its dynamic capabilities.
Another existing approach for mitigating voltage variations in the power network varies the reactive power according to Q-V characteristics (or Q-V curve), where a reactive power ‘Q’ is calculated as a function of a voltage ‘V’ measured at a point of interconnection (POI). However, in this approach, the controller may undesirably interact with other reactive power sources, as well as with other voltage regulating devices in the electrical power network. Also, in this approach, voltage variations caused by loads and other power generating devices may be compensated, which is undesirable.
In yet another approach, the reactive power may be varied according to Q-P characteristics (or Q-P curve), where the reactive power ‘Q’ is calculated as a function of an active power ‘P’ injected by a power generating source into the electrical power network. This approach compensates for only self-induced voltage variation, instead of compensating for the reactive power demand of the loads and other generating devices. This approach may however have an unwanted impact on the system since this approach may compensate for voltage rise when low voltage conditions exist, for example, during peak load conditions. The voltage rise caused by the power injection may be beneficial to improve the low voltage conditions. However, due to dependence on the injected active power ‘P’ alone, regardless of the state of the voltage at the POI for compensation, the controller may observe an increase in the active power ‘P’ and therefore may provide reactive power compensation even though it is not required. This approach may therefore lead to needless increased losses, both in the network and the power source, due to unnecessary compensation.
Hence, there is a need for an improved reactive compensation system and method to address the aforementioned issues.